92 PHILOSOPHICAL SOCIETY OF WASHINGTON. 
tity e, in the formula last given, all disadvantages from its want of 
exact accordance with observation disappear, and the results are 
brought far within the needful limits of accuracy. 
Mr. GILBERT then stated 
A CONCRETE PROBLEM IN HYDROSTATICS, 
suggested by the fact that the shore-line of a quaternary lake in 
the Great Basin is shown by levels to be more than a hundred feet 
higher on elevated land, that once formed islands near its middle 
part, than on the margin of the lake. This inland sea, known.as 
Lake Bonneville, was one hundred and twenty miles across. Among 
the possible explanations of the present difference of level, the 
effect of the removal of a large body of water in changing the form 
of level surfaces in its basin had been suggested, and the problem 
was to find how great an effect was due to this cause. 
In the discussion that followed, Mr. Paut called attention to the 
complexity of the calculation of equipotential surfaces. 
Mr. Woopwarp had formerly made a somewhat similar compu- 
tation to ascertain the deflection of the plumb-line caused by un- 
equal local attraction to eastward and to westward at the eastern 
end of Lake Ontario; from which it appeared to result that the 
effect due to this cause was insignificant in comparison with that 
required by the problem. 
Other remarks were made by Messrs. Dootttri4, Hri1, H. Far- 
QUHAR, and S. J. Brown. 
At the request of the Chairman, a communication promised by 
him was postponed until next meeting. 
